VEGF enhances intraneural angiogenesis and improves nerve regeneration after axotomy

Whilst there is an increased understanding of the cell biology of nerve reg eneration, it remains unclear whether there is a direct interrelationship b etween vascularisation and efficacy of nerve regeneration within a nerve co nduit. To establish this is important as in clinical surgery peripheral ner ve conduit grafting has been widely investigated as a possible alternative to the use of nerve autografts. The aim of this study was to assess whether vascular endothelial growth factor (VEGF), a highly specific endothelial c ell mitogen, can enhance vascularisation and, indirectly, axonal regenerati on within a silicone nerve regeneration chamber. Chambers containing VEGF ( 500-700 ng/ml) in a laminin-based gel (Matrigel) were inserted into 1 cm ra t sciatic nerve defects and nerve regeneration examined in relation to angi ogenesis between 5 and 180 d. Longitudinal sections were stained with antib odies against endothelial cells (RECA-1), axons (neurofilament) and Schwann cells (S-100) to follow the progression of vascular and neural elements. C omputerised image analysis demonstrated that the addition of VEGF significa ntly increased blood vessel penetration within the chamber from d 5, and by d 10 this correlated with an increase of axonal regeneration and Schwann c ell migration. The pattern of increased nerve regeneration due to VEGF admi nistration was maintained up to 180 d, when myelinated axon counts were inc reased by 78% compared with plain Matrigel control. Furthermore the dose-re sponse of blood vessel regeneration to VEGF was clearly reflected in the in crease of axonal regrowth and Schwann cell proliferation, indicating the cl ose relationship between regenerating nerves and blood vessels within the c hamber. Target organ reinnervation was enhanced by VEGF at 180 d as measure d through the recovery of gastrocnemius muscle weights and footpad axonal t erminal density, the latter showing a significant increase over controls (P < 0.05). The results demonstrate an overall relationship between increased vascularisation and enhanced nerve regeneration within an acellular condui t, and highlight the interdependence of the 2 processes.